The present invention is related to the field of pumps. More particularly, the present invention is related to submersible pumps.
Submersible pumps are designed to allow both the pump section and the motor section to be submersed in a liquid or slurry, such as, for example, waste water contaminated with abrasive solids or sewage. In general, the original concept of the submersible pump comprised two basic functional sections, a pump section and a drive section. The pump section typically comprises a casing or housing having an impeller disposed therein, which transfers energy to the fluid. The casing includes a suction opening and a discharge opening to facilitate fluid flow through the pump. The drive section typically comprises a motor having a motor shaft that provides rotational movement to the impeller.
In the original submersible pump concept, the pump section and the drive section are connected in close proximity to each other and completely submerged in the liquid being pumped. An electrical cable is typically extended to a power supply of the motor above the surface of the liquid. The motor components, such as the rotor, stator and other electrical components and connections are typically sealed in a watertight housing. A sealing arrangement is also provided to accommodate the motor shaft that extends through an aperture in the housing.
A drawback to the original concept of submersible pumps was the difficulty in determining a failure in the sealing arrangement. Since the pump is submerged, a seal failure was not detected until the motor had shorted out due to the liquid migrating from the pump section to the motor housing. Therefore, in later designs, an intermediate chamber was incorporated between the motor housing and the pump section. The chamber is typically filled with a barrier fluid and includes two sealing arrangements disposed therein. One of the sealing arrangements is utilized at one end near the motor housing to keep the barrier fluid out of the motor housing (also commonly referred to as a motor seal, inner seal, or upper seal in a vertical pump arrangement). The other sealing arrangement is utilized at the other end to keep the pumped liquid out of the chamber (also commonly referred to as a chamber seal, outer seal, or lower seal in a vertical pump arrangement). The barrier fluid acts as a lubricant and coolant for the sealing arrangements. Additionally, the barrier fluid is part of a moisture sensing system. Since the barrier fluid is typically a nonconductive mineral, such as an oil, or a synthetic hydrocarbon, a change in conductivity caused by the introduction of a pumped liquid, which is typically conductive, can be measured to indicate an outer seal failure.
The introduction of the intermediate chamber section led to other problems. The added length of the intermediate chamber required additional length of the motor shaft. This additional length of the shaft created an increased distance from the bearings of the motor to the impeller (typically referred to as overhang). In submersible pump applications, loads on the impeller, which cause loads on the motor shaft, can be significant. The loads cause deflection of the shaft and create stability problems, which result in increased deterioration of the sealing elements in the chamber section. The deflection of the shaft is dependent on many factors, including, the shaft diameter and distance between the support bearings of the motor, the shaft diameter and overhang (distance) from the bearing closest to the impeller to the load point at the impeller, and the magnitude of the radial load at the impeller. Since slurry pump designs provide larger and more robust impeller designs, this results in higher radial impeller loads. While the typical submersible motor has a support bearing arrangement for the motor shaft, this arrangement is often inadequate for these increased loads. Additionally, since the motor shaft serves as both a motor shaft and a pump shaft, other components of the motor need to be designed to handle the increased loads. In many cases, it is not practical to provide a commercially viable product that can solve the problems as explained above.
Certain other drawbacks exist with present industrial submersible pumps. Most notable is the lack of modularity with respect to the functional pump sections. In these designs, the motor is not independently separable from the remaining sections of the pump. Thus, even if the motor is the only component that needs to be repaired or replaced, the entire bearing, seal and shaft assembly must remain with the motor. Additionally, these pumps do not have independently separable bearing and sealing arrangements. Without an increased level of modularity, various components of these pumps cannot be quickly and individually replaced in lieu of completely replacing the pump or significantly repairing sections of the pump.
The lack of modularity also creates other maintenance issues. Many industrial and municipal plants no longer perform in-house maintenance particularly on electrical apparatus. Since the motor, motor shaft (which extends from the motor to the pump section) and seals are not designed to be separable in a modular sense, any failure of the pump, whether the failure ends up to be an electrical failure or a mechanical failure, generally results in the entire pump being sent to a motor rewind or repair shop. Due to lack of modularity, however, the motor shop must also be experienced in evaluation and repair of mechanical seals, shafts, bearings and other intricate components. Many of the motor repair shops cannot adequately provide repair for all of the pump components. They typically do not have the proper expertise to provide optimal quality repair for all components. This affects the cost, quality and turn around time for many repairs.
Another drawback with existing submersible pump designs for heavy duty applications is the sealing arrangements within the intermediate chamber. Most designs incorporate a tandem seal arrangement of an inner seal (motor seal) and an outer seal (chamber seal). With a very common arrangement, the outer seal has a stationary face at its top section and a rotary section including a rotary face that hangs down below the top section. A rotary spring is also included in the rotary section. However, because the spring is incorporated in the rotary section, it is susceptible to wear and fouling by material found within the liquid or slurry being pumped. These spring components are fragile. While some designs incorporate a guard or deflector around the rotary seal components, these designs are not completely effective. Another problem with tandem seal arrangements is that the lower seal is typically inadequately lubricated and cooled by the fluid within the chamber when the sump level drops below the outer (chamber) seal faces, thus causing seal failure. Other designs invert the lower seal in a back-to-back arrangement so that the rotary seal components are disposed within the intermediate chamber. However, these designs still place the stationary face at the bottom, where solid material can become lodged between the shaft and the stationary face. In addition, with this seal face arrangement on the lower seal, centrifugal force can also force particles from the fluid being pumped through the seal faces and into the oil chamber.
Thus, there remains a need for an improved submersible pump that can be used for in-plant industrial applications. Bore-hole pumps, for example, are longer/thinner pump designs that are designed to be inserted into wells. As the wells are typically narrow, the pumps have lateral constraints and therefore must have a slender, thinner design. Because of the required length of the pump, the pump must also have multiple stages to successfully pump fluid out of the well. A submersible pump suitable for in-plant industrial applications does not require multiple stages nor does it have lateral constraints. In-plant pumps, however, are often used in shallow sumps which have vertical constraints. The pump must be submersed in the shallow sumps for proper operation. The pumps, therefore, cannot have a long/slender design such as bore-hole pumps. Due to these requirements, in-plant pumps have lacked a desirable level of modularity to improve pump operation and maintenance.
The present invention is provided to solve these problems as well as other problems.
The present invention is directed to a modular submersible pump comprising a motor including a motor frame and a motor shaft, a bearing frame removably connected to the motor frame of the motor, a removable cartridge disposed within the bearing frame and having a shaft extension connected to the motor shaft. The cartridge includes at least one bearing and at least one seal in communication with the shaft extension. A pump case is removably connected to the bearing frame and having an impeller disposed therein, the impeller connected to the shaft extension of the removable cartridge.
According to another aspect of the invention, the removable cartridge disposed within the bearing frame includes a bearing housing having an interior chamber, a seal housing having an interior chamber and removably connected to the bearing housing, and a shaft extension connected to the motor shaft and extending through the interior chambers of the bearing housing and the seal housing. The bearing housing has at least one axial bearing and at least one radial bearing disposed therein and capable of bearing against the shaft extension. The seal housing has at least one seal disposed therein, the seal including a rotary seal face and a stationary seal face, the rotary seal face connected to a shaft sleeve concentrically disposed around the shaft extension, the stationary seal face being spring-loaded against the rotary seal face and attached to the interior portion of the seal housing.
According to yet another aspect of the invention, the modular pump further includes an expeller rotor connected to the shaft extension for rotation therewith, the expeller rotor is disposed adjacent to the seal housing and the pump case. The expeller rotor acts to dispel matter within a pumping liquid away from the seal housing.
According to yet another aspect of the invention, the interior portion of the seal housing has an axial length and the interior portion of the bearing housing has an axial length, the axial length of the interior portion of the seal housing being less than the axial length of the interior portion of the bearing housing. The short length of the seal housing minimizes shaft overhang from a lower radial bearing in the bearing housing to the impeller.
These and other aspects of the present invention will be readily apparent after review of the detailed description in conjunction with the drawings.